Reflectivity enhanced refractive index sensor based on a fiber-integrated Fabry-Perot microresonator

Abstract

We discuss a fiber-integrated refractive index sensor with strongly improved detection performance. The resonator has been implemented by means of focused-ion beam milling of a step index fiber and shows a sensitivity of about 1.15µm/RIU. Coating the resonator walls led to a strongly improved mirror reflectivity by a factor of about 26. Design rules for device optimization and a detailed mathematical analysis are discussed, revealing that the sensor operates as an optimized Fabry-Perot resonator. We also show that the performance of such kind of Fabry-Perot sensors is, in general, limited by the detection limit function - a quantity depending on the cavitiy's finesse and on the measurement capabilities used.

Simultaneous measurement of temperature and refractive index using focused ion beam milled Fabry-Perot cavities in optical fiber micro-tips

“…Micromachining is a more recent technique that allows for the creation of very small cavities or microcavities. The two prominent techniques for optical fiber micromachining are femtosecond laser micromachining [11][12][13][14][15][16][17] and focused ion beam (FIB) milling [18][19][20][21][22][23]. Femtosecond (fs) laser micromachining has been used to create cavities in several ways.…”

“…Preliminary work on microcavities milled with FIB has been presented, where cavities have been fabricated in tapered fiber tips for either temperature [18] or refractive index sensing [19,23]. Cavities in microwires for temperature and vibration sensing have been shown [20] as well as focused ion beam milled cavities in polished optical fibers [21]. FIB milling has even been demonstrated in exposed-core suspended core fibers [24].…”

Recent Developments in Micro-Structured Fiber Optic Sensors

“…The cantilever FP structure was sensitive to vibrations and able to measure frequencies in the range of 1Hz to 40 kHz. Coating was also put onto the FPI walls to increase the mirror reflectivity by a factor of about 26 [211], which has been demonstrated with a high sensitivity on a wide RI measurement range [212]. Recently, a multi-cavity structure was fabricated by the FIB technique by combining the concepts of solid silica cavity and gap cavity [207].…”

Chemical and biochemical sensing applications of microstructured optical fiber‐based systems

“…For example, two polished fiber end faces can be hosted in a holey sleeve, but this assembly is complicated, requiring other materials such as epoxy resins, and also has a strong dependence on temperature . Other more recent approaches consist of chemical etching or laser micromachining . The latter process was employed to create a FPR that is showed in Fig.…”